The present invention generally relates to shock absorber housings for shock absorbers of a vehicle.
More specifically, the present invention relates to a shock absorber housing for a shock absorber of the type having a tube, which has a tubular wall, and an attaching element joined onto the tubular wall, the attaching element determining a critical force introduction area of a force transmission from the attaching element into the tubular wall.
In vehicles, shock absorbers serve for protection against impact shocks and vibrations due to uneven road surfaces and for damping these. In vehicle construction, shock absorbers are also referred to synonymously as vibration dampers.
The tube of the shock absorber housing serves to accommodate the damper components, such as piston, valves, piston rod etc.
At least one attaching element is usually provided on the outside of the tube. The attaching element can here be designed to fix the tube and hence the shock absorber to the vehicle structure, in particular to the wheel suspension or to the wheel of a vehicle.
The attaching element may also be designed, however, to support a plate, in particular a spring plate, on the shock absorber housing.
In both of the configurations of an attaching element described above forces, which are concentrated locally in a critical force introduction area, are transmitted to the tubular wall of the tube by said element during operation of the vehicle. Where the attaching element serves for fixing the tube to the vehicle structure, the critical force introduction area is situated in the area of the upper axial end of the connection between this attaching element and the tubular wall. If the attaching element serves to support a plate on the tubular wall of the shock absorber housing, the critical force introduction area is distributed annularly around the tubular wall. In both of the aforementioned cases the critical force introduction area, viewed over the length of the tube, extends only to a small partial length of the tubular wall. In the critical force introduction area of the tubular wall the tube is subjected to high bending forces, which can lead to buckling or tearing of the tube at this point.
In conventional shock absorber housings the tube as a whole is formed integrally or in one piece over the entire length of the tube. The wall thickness of this one-piece tube is in this case dimensioned so that the tubular wall in the critical force introduction area is strong enough to prevent buckling or tearing of the tubular wall in this area. For this purpose a considerable wall thickness of the tubular wall is necessary in this area. Since the tube overall is of one-piece construction, however, the tubes are formed with this comparatively large wall thickness over their entire length, or the attaching element(s) are made of more elaborate, in particular stronger, design for a more uniformly distributed introduction of the forces into the tubular wall. This has the disadvantage that the shock absorber housing has a high weight. In vehicle construction, however, weight-saving is a significant factor, not least also because of the desire to reduce the energy consumption through a lower weight.
A shock absorber housing is disclosed by the German company booklet “ThyssenKrupp Steel Fachpresse Forum 2006—Tailored Orbitals”, 2006.
A further shock absorber housing is disclosed by the German press article “Tailored Orbitals—Einsatzmöglichkeiten and Perspektiven” in ATZ, Issue 10/2007, Volume 109, 2007.
In the aforementioned German company booklet and in the aforementioned German press article it is proposed to address this problem by building up the tube of a shock absorber housing from more than one tube section, the tube sections being joined together in the longitudinal direction of the tube. As is described there, building up the tube from a plurality of tube sections affords the advantage that the various tube sections may have different wall thicknesses, that is to say those tube sections which are subjected to greater forces in operation are manufactured with a larger wall thickness, and those tube sections which are only subjected to a lesser force are correspondingly manufactured with a smaller wall thickness. As is described in the aforementioned German press article, the tube of a shock absorber tube may be constructed from a total of three tube sections, the two end tube sections having a larger wall thickness and the middle tube section having only a reduced wall thickness compared to these. Besides the advantage of a weight-saving, this also saves on material costs, since these are reduced due to the tube in one section being designed with a smaller wall thickness.
In both of the aforementioned documents on the prior art the individual tube sections are butt-welded, that is to say they are placed end-to-end against one another and if necessary also pressed axially against one another prior to the butt-welding.
Despite the weight- and cost-saving in the case of the tubes of shock absorber housings disclosed in both of the documents cited above, these carry the disadvantage that at least some individual tube sections are provided, which still have a large wall thickness, for example that end tube section, which according to both of the aforementioned documents serves to receive the fork. Another disadvantage to these known tubes of shock absorber tubes is that the individual tube sections are welded with the rim faces of their ends against one another, with the result that in the area of these joints there is no increased resistance to forces introduced precisely at the joint.